Restoration of impaired immune functions of aged animals by chronic bestatin treatment.

An attempt to correct the state of immunodeficiency in old age was made by repeatedly injecting a chemically defined immunostimulating agent, bestatin, to 16 month old (C57Bl/6 x BALB/c) F1 mice. Aged mice were found to have depressed T-cell and B-cell responses but increased ADCC activity. Weekly injections of bestatin over a period of 6 months resulted in varying effects depending on the dose administered. Small doses (10 microgram per injection) were more effective in restoring humoral responses to SRBC rather than delayed-type hypersensitivity reactions, whereas large doses (100 microgram per injection) acted in the opposite way. Macrophage activation was only obtained after the administration of the high doses of bestatin. Continuous treatment with bestatin did not prevent the appearance of suppressor cells induced by ageing. It led to a significant reduction of ADCC activity in aged animals near to the base line value of young animals. Animals were examined for the presence of spontaneous tumours from the end of the treatment until the age of 28 months. A significant reduction of spontaneous tumour incidence was observed in mice given repeated injections of 100 microgram bestatin when compared to untreated aged mice and to mice given the low doses of bestatin.